How to tell if its live rock?

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I am going to look at a members live rock, that's why I was asking. I have faith in the LFS that I deal with, but i don't want to pay $9/lb expecially when this is my first saltwater set up and I'm not ever sure if this is the hobby for me. I have a thing for fresh water but I think salt water is very nice to look at, so just getting my feet wet.